As an introduction to problems solved by the present invention, consider the conventional electrophotographic printer employed in office computing systems, facsimile receivers, office copiers and the like. Such a printer typically includes one or more input trays for paper on which to print. Although some printers are designed to operate exclusively with one type of print media, contemporary users are demanding the versatility to print on a wide variety of sheet media including papers that are colored, coated, or otherwise treated, overhead transparencies, plastic sheet, and other resin films, to name a few examples. Methods of achieving high resolution, permanent, high-speed print on these media vary, however.
Conventional printers equipped with media sensors discriminate among media only when media are widely different, such as discriminating a transparency from opaque paper. In such printers, a signal from the sensor affects a selection of a print mode among several built-in print modes. Neither the method of sensing nor the method of selection is accurate or repeatable enough to adjust high quality printing on papers having slight variations in surface gloss.
Inaccuracy and non-repeatability are attributable to many factors. When light sources and sensors are used to make surface measurements, thermal and aging factors degrade measurement accuracy. Thermal factors degrade alignment, adversely affecting accuracy. Because temperature within a printer varies greatly during operation, thermal factors, degrade repeatability. Furthermore, within the conventional printer, debris including toner, paper fragments, and dirt may temporarily or permanently build on portions of the measurement system, making measurements inaccurate and non-repeatable.
The market for high resolution, permanent, high-speed printers is already large and growing with the increase in computing power available at decreasing cost. In addition, the variety of media available to the user is increasing as the user increases in sophistication. Heretofore, only book and periodical publishers and professional printers were concerned with presenting printed results on a media of selected gloss appearance. Now, however, users are expecting to be able to produce equivalent results on sequential sheets of any media used professionally, with little or no intervention with the printing method.
In view of the problems described above and related problems that consequently become apparent to those skilled in the applicable arts, the need remains in printers and in systems for printing an image on media for accurate measurement of the media surface in order to govern printing for higher quality results.